Aluminum alloys are used in making sheet metal automotive body panels and other parts. In many such applications the aluminum part requires a decorative and wear resistant surface. Usually such aluminum parts are simply painted to match other surfaces on the vehicle. The painted aluminum surface is attractive and provides wear resistance that is comparable to other painted surfaces on the vehicle. Aluminum surfaces can also be anodized and the resulting oxide layer colored. But it has proven difficult to produce a colored anodized layer on an aluminum part that is both decorative for automotive applications and suitably wear resistant.
The state of the art is such that anodized surfaces that can be colored have not been resistant to wear or scratching. The clear, porous anodized layers that will reliably, reproducibly and uniformly take a coloring material (e.g., a pigment) are too soft for vehicle applications. But anodized coatings that are very hard are dark and are not receptive to coloring for vehicle surfaces.
Thus, it is an object of the present invention to provide a method of producing a wear resistant anodized surface on an aluminum alloy automotive body part that can suitably be colored.